Stereo-regular crystalline polyolefins made from Ziegler type catalysts; i.e., transition metal catalysts, particularly polypropylene which is substantially isotactic, have enjoyed phenominal growth. They are used to produce shaped articles varying from fibers to toys.
Crystalline polymers in their usual form, from the reactor have many outstandingly good properties and some undesirable ones. For example, the outstanding desirable properties of crystalline polypropylene are high tensile strength and substantial hardness. A disadvantage of the highly crystalline polypropylene is a lack of transparency or clarity, which shows up as opacity or translucency in fairly thick articles and as haze in thin films.
Highly crystalline polypropylene has another congenital disadvantage, which is its relatively low impact resistance, particularly at low temperatures.
It is known within the art that the problems with opacity and haze can be alleviated to a large extent with the addition of certain materials to the polymer, which are termed nucleating agents. These apparently modify the crystallization process, particularly in altering the size of the spherulites formed upon crystallization.
Generally speaking, the materials known to the art for nucleation purposes are either very small, finely divided solid inorganic materials, such as silica, or they are organic fatty carboxylic or polycarboxylic acids and derivatives thereof. Relevant prior art patents include U.S. Pat. Nos. 2,991,264; 3,517,086, 3,207,735-739.
U.S. Pat. No. 3,483,276 shows maleic anhydride grafted polypropylene dispersed in homopolypropylene, but there is no teaching that this nucleates. And indeed, data presented herein shows that maleic anhydride grafts do not nucleate.